Neurofibromatos is type 1 (NF1) is one of the most common inherited disorders and is characterized by abnormalities in multiple tissues derived from the neural crest. The NF-1 gene has been cloned and mapped to human chromosome 17q11.2. The NF-1 gene has an open reading frame that predicts a protein consisting of 2,818 amino acids, known as neurofibromin. Here, we report two kinds of novel frame shift mutations of the NF1 gene from 2 out of 56 unrelated Korean NF1 patients. These mutations were detected using polymerase chain reaction and single strand conformational polymorphism analysis. Sequencing analysis revealed four base pair insertion at codon 1270 of exon 22, and a base pair deletion at codon 1398 of exon 24. These mutations resulted in premature termination of the mutant alleles and may encode truncated forms of neurofibromin.